The dissociative ionization of 17 Schiff bases obtained from 2(4)-azafluorenones and linear benzo-1,4-diazafluorenone was investigated. The intensities of the [M-H]+ and [M-CH3]1 ion peaks depend on the structures of the ketone and imine parts of the molecules and are determined by the possibility of the occurrence of cyclization processes with the participation of their structural elements. The fragmentation of the investigated azomethines is also accompanied by the elimination of an NR particle and a hydrocarbon R radical by the molecular ions. This process takes place most easily when a cyclohexyl substituent is present in the imine fragment. In contrast to previously investigated azomethines, the loss of an HCN molecule by the M+ ion occurs without participation of the exocyclic nitrogen atom. © 1981 Plenum Publishing Corporation.